1. Field of the Invention
Most natural and processed foods contain one or more of intact protein, predigested protein (protein hydrolysates), amino acids and non-protein nitrogen. These nutrients are the building blocks of lean body mass (protein) and other nitrogen containing metabolites (for example, enzymes, vitamins, hormones, etc.). Carbohydrates normally present in foods can be simple (for example, dextrose, fructose, etc.) or very complex in nature (for example, fiber, pectin, starch, predigested starch [hydrolyzed cereal solids, dextrose oliogosaccharides, etc.], dextrin, etc.). Carbohydrates in foods supply energy, and desirable psychosensory benefits, such as taste and texture.
This invention concerns essentially residue free dietary compositions for supplying nitrogen nutritional requirements to users whose normal digestive processes are imparied as, for example, patients in catabolic disease states such as duodenal fistula, the short gut syndrome, pancreatitis, ulcerative colitis, and the like, as well as to pre- and post operative patients who are required to eliminate temporarily solid residues from their diet because of surgical intervention. The low residue compositions, designed to be readily absorbed in the duodenum and jejunum, result in minimal intestinal digestive activity and reduced frequency of defecation, with the quantity of fecal matter reduced to essentially endogenous amounts.
More particularly, the invention concerns solid dietary compositions (or concentrates) comprising at least one amino acid or other nitrogen containing material (nitrogen compound) and at least one carbonyl group-containing material (carbonyl compound) such as a reducing sugar, in admixture therewith, wherein the shelf life of the composition is extended by separating the nitrogen compound from the carbonyl compound with another, non-nitrogenous, relatively non-reducing ingredient of the dietary composition, namely a starch having a D.E. (Dextrose Equivalent) number of from 0 to about 24 so as to prevent or retard the Maillard-type browning reaction (hereinafter "Maillard reaction") between the nitrogen compound and the carbonyl group containing material. As used herein, the term starch includes the native starches and their derivatives (e.g. dextrin or chemically or enzymatically modified starch, commercially available as dextrose [or glucose] polymer, dextrose [or glucose] oligosaccharides, corn syrup solids, hydrolyzed starch or hydrolyzed cereal solids). By the expression "carbonyl group-containing material" or "carbonyl compound" as used herein is meant a compound wherein the carbonyl group is either a keto or aldehyde group. In accordance with the invention, the reactive compounds are separated by interposing the starch between the reactive components, typically by coating one or both of the nitrogen-containing material and the carbonyl group-containing material with the starch.
Many synthetic foods and special dietary products exist which contain, among other nutrients, amino nitrogen-containing (proteinaceous) compounds (e.g. one or more free amino acids or their salt derivatives, protein hydrolysates, intact whole proteins, or a combination of these) plus vitamins, including amino nitrogen containing vitamins, e.g. para-amino-benzoic acid (PABA), thiamine, niacin, choline, riboflavin, ascorbic acid, etc. and their derivatives, plus other, non-amino nitrogen-containing compounds, e.g. ammonium compounds such as ammonium sulfate, plus carbohydrates, including reducing sugars, e.g. glucose (also known as dextrose), fructose (also known as levulose) and 5-carbon or pentose sugars such as xylitol (also commonly called xylose), and other aldehyde containing compounds which may be found, for example in flavoring agents. Even non-reducing disaccharide sugars (e.g. sucrose, lactose, maltose, and their derivatives) may be hydrolyzed catalytically to produce the reducing sugar moiety, this reaction being promoted by the presence of moisture and elevated temperatures.
Over time, in the presence of moisture, and in even moderate heat (i.e. at temperatures above the freezing point of water), the Maillard/browning reaction results from the interaction of the nitrogen compounds with the aldehyde groups of the reducing sugars or other carbonyl compounds.
In some instances, a "browning" reaction is desirable -- for example with butterscotch confections, caramel, cooked meats, etc. In other instances this reaction is objectionable -- for example with fluid and dried milk and with special dietary products containing amino acids, hydrolyzed protein or intact protein.
When browning occurs in, for example, an elemental diet (a white powder composed of purified amino acids, carbohydrate, fat, vitamins, minerals and flavorings which, when reconstituted with water to a beverage, semi-solid or solid food, provides all nutrients known to be essential to the suport of human life) or in any other form of nutrient defined diet, the resulting color change can be expected to be found objectionable by users. So, too, can the concomitant changed organoleptic qualities, for example, a bitter, metallic taste and an associated acrid, pungent odor. Even more important, the Maillard reaction can actually alter the nutritional values of the product. For example, chemical analysis of such a total elemental diet which had undergone the Maillard reaction while being aged 24 months at 40.degree. F. (4.4.degree. C.) showed a reduction in the level of PABA to 40% below the amount contained in the product at the time of manufacture.
Such elemental diets are described, for example, in U.S. Pat. Nos. 3,773,930, issued Nov. 20, 1973, entitled "Amino Acid Compositions" and 3,821,432, issued June 28, 1974, entitled "Bland Amino Acid Compositions." They contain, among other nutrients, a blend of purified amino acids, free glucose and PABA. Other special dietary foods have been developed which contain amino acids, protein hydrolysates and whole protein, singly or in combination, as well as reducing sugars and, optionally, nitrogen containing vitamins. All of these dietary foods have been shown to suffer from short shelf lives of from six months to one year when stored at ambient temperatures (up to about 86.degree. F. [30.degree. C.]). This has been true even when product moisture levels have been reduced to less than 2% and expensive moisture barrier laminates have been used for packaging. Generally, the higher the finished product temperature and moisture content, the more pronounced or rapid the resultant Maillard reaction will be.
2. Description of the Prior Art
The Maillard reaction has been recognized as a limiting factor on the shelf-life of compositions with which the present invention is concerned, including concentrated elemental diets, since it takes place even when the reactants are in contact in the powdered form in the presence of some moisture (even less than 2%) and even at sub-ambient temperatures. Previous attempts to deal with the problem have not been entirely satisfactory, particularly for powdered elemental diets, and the problem still persists.
U.S. Pat. No. 2,426,634, issued Sept. 2, 1947 to Daniel Melnick, is concerned with enhancing the shelf-life of concentrated food preparations, such as dehydrated soup mixes, by physically separating the amino acid materials from the carbohydrate materials, or by rendering the mix sufficiently acid to inhibit the reaction, or by a combination of these techniques. At column 3, there are presented the general conclusions that darkening (browning, or pigment formation) is enhanced by alkaline conditions, the more alkaline amino acid materials being more reactive. Also, the simpler carbohydrates, the mono- and di-saccharides are disclosed to react more rapidly with the amino acid compounds than the more complex carbohydrates, starches reacting so slowly as to be a negligible factor over "normal storage periods."
The patentee suggests enclosing the dextrose or the amino acid materials in a sheath of methyl or ethyl cellulose or fat or "other materials which will readily dissolve or disperse when the mass is mixed with hot water . . . " While fat may be a natural ingredient of concentrated food, as a coating material it tends to cause flotation in water and is difficult to dissolve. Ethyl and methyl cellulose are not necessary or usual ingredients of an elemental diet. Moreover, the heating required to dissolve the coating of this patent is unacceptable for certain dietary compositions, particularly those containing vitamins, since the nutritional value of such heat sensitive components is thereby adversely affected.
As indicated by the patentee of U.S. Pat. No. 2,305,940, discussed hereinafter, pH adjustment requires care, and presents the risk of adversely affecting taste. The addition of ethyl or methyl cellulose, ingredients not otherwise necessary or desirable in a concentrated elemental diet, could cause other complications in some patients already suffering from abnormal gastric conditions as, for example, patients requiring a low fecal residue diet.
The preparation of a substantially non-hydroscopic edible spray-dried powdery material for use in the baking, brewing and confectionary industries is accomplished in accordance with U.S. Pat. No. 2,305,940, issued Dec. 22, 1946 to J. F. Walsh, by intimately mixing a starch conversion syrup having reducing sugar content of 25% to 65% with a steep water filtrate containing soluble protein, optionally adding diastase, heating to a temperature of about 125.degree. F. (52.degree. C.) to about 150.degree. F. (66.degree. C.) at a pH in the range of about 4.5 to 6.5 to condition the mixture for spray drying without developing any darkening or browning, and then spray-drying the mixture at a temperature not exceeding 150.degree. F. (66.degree. C.) to a moisture content not substantially above 3%. This does not, however, effect a separation between the reducing sugars and the protein of the steep water. Rather as a result of this process, they remain intimately admixed in the spray-dried product.
The use of hydrolyzed cereal solids (starch) having a low D.E. number as a coating for a synthetic cheese or similar product comprising edible fat, a flaked starch carrier, a flavoring agent and, optionally, a coloring agent is shown in U.S. Pat. No. 3,689,290, issued Sept. 5, 1972 to Blackstock et al. The disclosed product appears to contain no protein; and all of the ingredients are mixed together, the entire mix being coated by the low D.E. starch particles.
The problem of preventing the Maillard reaction in synthetic dietary compositions is also dealt with, inter alia in U.S. Pat. No. 3,950,547, issued Apr. 13, 1976 to P. L. Lamar III et al. The patentees, however, teach only to use the less reactive peptides rather than free amino acids and to avoid the presence of reducing sugars in their compositions. However, it is often necessary or desirable to have significant amounts of uncombined amino acids present in the dietary compositions with which the present invention is concerned in order to obtain the exact amino acid profile desired for the nutritional management of certain disease states (e.g. short gut syndrome, kidney and liver dysfunction, inflammatory bowel diseases and inborn metabolic disorders) and to use reducing sugars to provide a readily absorbable and metabolizable carbohydrate, for traumatized and other diseased patients lacking the enzyme disaccharidase, while providing organoleptic properties desired for oral consumption.
The patentees (of U.S. Pat. No. 3,950,547) also disclose and claim the use of specified amounts of high amylose starch in their compositions in order to improve the emulsion stability thereof. However, they do not use starch (or any other material) to separate the components of their compositions that take part in the Maillard reaction.
U.S. Pat. No. 3,962,416, issued June 8, 1976 to S. Kutzen, teaches protecting nutrients, including proteins and other nitrogen containing materials, by encapsulating them in an enteric coating comprising a high protein vegetable material which can contain no more than 40% by weight of non-protein material and which can include starch. The coating is dissolved in the digestive system. Not only is this coating different from that of the present invention, it is unsuitable for use in concentrates of complete elemental diets intended for immediate and complete dissolution or dispersion in water prior to consumption by the user either orally or via tube, the latter requiring a fluid of low viscosity and no, or only very fine, particulate matter. In addition, the enteric coating would retard the rapid absorption necessary for patients with reduced digestive and absorptive capacity in the digestive system (e.g. bowel resections) who would use elemental diets such as those with which the present invention is concerned.
In describing an improved method for encapsulating a condiment by spray drying, U.S. Pat. No. 3,985,913, issued Oct. 12, 1976, to Johnson et al., discloses that the condiment can be, inter alia, a proteinaceous material, and that the coating material can be hydrolyzed cereal solids. In this process, the entire condiment is coated with the hydrolyzed starch, and the process does not result in, nor is it intended for, separation of proteinaceous material of a dry mix from a reducing sugar or other material thereof capable of undergoing the Maillard reaction with the proteinaceous material.
German Offenlegungsschrift No. 25 21 800, filed May 16, 1975, is concerned with the problem of preserving the stability of free amino acids in their passage through the rumen of a ruminant, and discloses covalently bonding the amino acids to intra- or inter-molecularly bridged carbohydrates and natural polyhydroxylic compounds, including both reducing and non-reducing sugars.
U.S. Pat. No. 3,697,287, issued Oct. 10, 1972 to M. Winitz postulates three major causes for objectionable taste in chemically defined diet formulations. These related causes are (1) the inclusion of amino acids or their derivatives which contain sulfhydryl groups; (2) the inclusion of amino acids or derivatives, such as glutamic acid, whose inherent taste is incompatible with the flavor of the remaining ingredients; and (3) the use of amino acids of their derivatives that have bad tasting impurities, such as methyl mercaptan, associated with them. The patentee discloses and claims that when such compositions, containing 0.26 gm of methionine per liter in a solution containing at least about 3 grams of essential amino acids per liter, contain methyl mercaptan in an amount not exceeding about 15 mg per liter, palatability of the product is improved.